<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<style>
  div{
    width: 100px;
    height: 100px;
    border: 1px solid red;
  }
  #d1{
      position: absolute;
      right: 0;
      bottom: 0;
  }
  #big{
      width: 200px;
      height: 200px;
      margin: 100px 0 0 100px;
      background-color: green;
      /*做参照物*/
      position: relative;

  }

  #big>div{
      width: 100px;
      height: 100px;
      background-color: blue;
      margin: 50px 0 0 50px;
  }

  #big>div>div{
      width: 50px;
      height: 50px;
      background-color: red;

      position: absolute;
      left: 0;
      top: 0;
  }
</style>
<body>
<div id = "big">
    <div>
        <div></div>
    </div>
</div>
<div id="d1">div1</div>
<div>div2</div>
<div>div3</div>


</body>
</html>